1. Field of the Invention
This invention relates to an analytical device for atmospheric analysis and, more specifically, to a device for detecting low concentrations of chemical vapors by use of a lasing dye sensor system.
2. Description of the Prior Art
In the past, detection of chemical vapors by means of a laser has been accomplished by monitoring or analyzing spectra of the sample gas. Previous devices and methods used a cavity which holds a sample gas or absorber media, such as a dye or a reference gas, to modify the laser beam to detect the presence of a particular chemical vapor.
Parli et al describes using intracavity absorption to detect hydrocarbons with a helium-neon laser operating at the 3.39 micron and 0.63 micron lines in the spectra ("Helium-Neon Laser Intracavity Absorption Detector for Gas Chromatography", Parli et al, Anal. Chem., Vol.54, p.1969, (1987)). Hydrocarbons absorb at 3.39 microns. The 0.63 micron line intensity is a quantitative measure of the concentration. However, only molecules which absorb at 3.39 microns or 0.63 microns can be detected with this method. No dye is used in this method as a absorption or reaction medium.
The use of dye in intracavity dye laser spectroscopy (IDLS) is known to give greater versatility over intracavity absorption since different dyes acting as absorbing media will give different modes in the spectra ("Intracavity Laser Tomography of C.sub.2 in a Oxyacetylene Flame, Harris and Weiner, Opt. Lett., Vol.6, p.434 (1981); "Power Dependence of Continuous Wave Intracavity Spectroscopy", Harris, Opt. Lett. Vol. 7, P.497 (1982)). However, the modes must be matched with the absorber to be detected. The number of modes obtained per dye is limited, so use is restricted. The dye is not chemically reactive with the sample gas.
Wolber (U.S. Pat. No. 3,732,017) teaches analyzing an unknown gas with a tunable laser having a known gas in the laser cavity so that the laser will lase only at the frequencies of the known gas. The unknown gas is illuminated with the reference spectrum of the known gas. Some or all of the peaks will be absorbed if the unknown gas is partially or completely composed of gases identical to the known gas. The use of a chemically reactive dye is not taught.
Giuliani (U.S. Pat. No. 4,513,087) teaches detecting small amounts of chemicals such as ammonia, hydrazine and pyridine with a capillary tube having the outer surface coated with a dye film such as oxazine perchlorate, which, when exposed to these chemicals, changes color. The capillary tube serves as a multiple total reflective medium for an optical beam from a light emitting diode. When the color of the coating changes, the multiply-reflected light in the tube is modified and the presence of the chemical is indicated by the change in output light intensity from the capillary tube. The device is reusable since removing the chemical from the presence of the dye restores the original color. Sensitivity is down to less than 60 ppm. Response time is not instantaneous but takes one to two minutes for the vapor to permeate into the coating and an equal amount of time for the color change to reverse so the detector can be reused.
A system which can detect small concentrations of chemical vapors and gases, can respond instantaneously and can be regenerated for reuse as needed. Simple operation for field use would also be an advantage over prior art.